If I remember correctly, at various really high scores, a gold block will drop on each stage. Destroying it will unlock a specific new challenge, and beating that challenge will give you the achievement.

I cannot get a gold block to drop for the life of me. I've had 5 games above 20k, and about 3 more between 15-20k, and another dozen above 10k on Troublesome Tech. Obviously, I'm also spending a whole lot of time at level 4 in those cases, and still nothing.

Is there anything special that needs to be done, or am I just crazy unlucky? I was at 100% before the update, so I can't imagine I'm missing something.

EDIT: After I posted this, I went on to the mansion. First time at level 4 over 10k, there's a golden block. No clue why I was having such crap luck on tech.